FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] Neurotransmitters are released from a specific site in the axon terminal called the active zone, which is composed of synaptic vesicles and a meshwork of cytoskeleton underlying the plasma membrane. The protein encoded by this gene is thought to be a scaffolding protein involved in organizing the presynaptic cytoskeleton. The gene is expressed primarily in neurons in the brain. A similar gene product in rodents is concentrated in the active zone of axon terminals and tightly associated with cytoskeletal structures, and is essential for regulating neurotransmitter release from a subset of synapses. [provided by RefSeq, Jul 2008] PHENOTYPE: Mutants lacking functional protein exhibit impaired hippocampal and photoreceptor synaptic transmission, aberrant photoreceptor ribbon synapse formation, and spontaneous epileptic seizures. [provided by MGI curators]